1. Field of the Invention
The invention pertains to connections to and from a digital circuit and, in particular, to input/output connections between a microprocessor and peripheral control devices used in photographic and video cameras.
2. Description Relative to the Prior Art
A microprocessor typically has a considerable number of signal-carrying ports devoted to input and output connections with peripheral devices. For example, in the case of a microprocessor-controlled camera, various solenoids (for releasing the shutter, controlling the diaphragm aperture, and the like) and various switches (for signalling the beginning of light measurement and shutter release, and the like) are connected to corresponding input and output ports of a microprocessor (see, for example, the connections to the microprocessor in the camera disclosed in U.S. Pat. No. 4,401,373). Ordinarily, each port corresponds to a connecting pin on an integrated circuit chip which bears the microprocessor. With many ports, therefore, there are many pins.
Large numbers of pins are not cost-effective since each additional pin represents additional cost in the manufacture of the microprocessor integrated circuit, additional labor in the connection of the pin to a peripheral device, and decreased reliability due to the additional connection. The numbers of pins can be reduced if the ports are made bidirectional, that is, capable of accommodating both incoming and outgoing exchanges with a peripheral device. Compared to a unidirectional port, however, a bidirectional port requires a more complex microprocessor architecture since the direction of the port has to be internally specified and implemented via additional internal digital processing elements.